This invention relates to photoelectric timing systems, and particularly to such systems employing pulsed invisible light beams for communicating a condition of time.
Timing systems for measuring elapsed times having light-beam activated start-stop gates are well known in the art. The design of these well known systems has proved disadvantageous for many applications and in certain situations these systems if usable are extremely inconvenient to use. For example, prior art timing systems using incandescent lamps for generating the light beam, normally require an external electrical power source to be connected to each start-stop gate, because incandescent lamps of sufficient intensity to provide an adequate light beam require large amounts of power. It is a great inconvenience to extend electrical power cables over the long distances which may separate the start and stop gates, particularly when the terrain is rugged or inaccessible, such as with a ski slope. For example, it may prove entirely impractical to supply electrical power when the gates are separated by stretches of water. Batteries of sufficient power to supply the incandescent lamps are bulky, heavy and difficult to transport and the use of such batteries as a power source is also inconvenient.
In prior art systems having incandescent light beams, the beam may not be of sufficient intensity to accurately communicate elapsed time in a variety of different atmospheric, weather or ambient conditions. An incandescent beam cannot penetrate fog or rain without diffusing. High intensity floodlights or bright sunshine may override the incandescent lamp beam preventing accurate registration of light-beam interruption. If timing must occur in total darkness, an incandescent system is not suitable since its light beam is visible and produces illumination. In addition, the incandescent beam generally lacks sufficient intensity to accurately penetrate the long distances necessary to form a wide start or finish line essential in some vehicle racing contests, for example. Another disadvantage of previous systems is that the incandescent lamps may easily burn out, resulting in an unnecessarily high probability of system malfunction. Accordingly, it is an object of this invention to provide an improved timing system which overcomes the foregoing disadvantages of the prior art.
It is another object of this invention to provide a timing system having start-stop gates which are portable, self-contained, internally energized and simple to handle, set-up and operate.
It is a further object of this invention to provide a timing system having start-stop gates employing a light beam of a quality and intensity which yields highly accurate timing even over long distances and in a variety of atmospheric, weather and ambient conditions.
It is still another object of this invention to provide a timing system which requires little attention, service or maintenance.
Briefly, in carrying out the objects of this invention in one embodiment thereof, each start-stop gate of the present invention employs a source of invisible light and at least one receiver for the invisible light. A light beam is formed by directly light from the light source to the light receiver, and when an object crosses and interrupts the light beam, the light receiver senses the interruption and communicates a signal to a counter-timer which indicates a condition of elapsed time. The light source includes solid state circuitry for providing a pulsating or modulated beam of high intensity, semi-coherent, invisible light. The light receiver, also of solid state circuitry, is a device adjusted for optimum reception of the light beam. The light receiver filters out all light signals other than the pulsating or modulating light beam and converts the light beam signal to a voltage. Interruption of the light beam has the effect at the light receiver of altering the pulsating frequency of the beam, and the light receiver rejects the altered frequency causing the voltage level to drop. A logic circuit monitoring the voltage level yields a digital signal when the voltage level drops which is communicated over a single conductor or over a radio communication link to the counter-timer for indicating a condition of elapsed time. The system includes means for facilitating the alignment of the light beam from the light source to the light receiver. Such means may provide an audible sensory signal of high volume when optimum alignment is attained, and it may also include a light emitting device for providing a visual sensory indication that the light source and light receiver are out of alignment.